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Name: Evren
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Question:
Hi, Why does friction not apply to gas molecules? My chemistry books says, "The collision of particles with each other or the walls of the container are perfectly elastic, no loss of energy occurs". How is "no loss of energy" possible when gravitation and friction applies to any matter on earth?



Replies:
To understand the answer to that question, you need to understand how friction works, and why energy is "lost" to friction when objects interact. Friction arises because objects are not single things, but instead are made of many tiny atoms. The bulk kinetic energy of the atoms all moving in the same direction is partitioned, in a collision, into the kinetic energy of the individual atoms moving in many different directions. The kinetic energy is still there, but as kinetic energy of individual atoms, not as the "translational" kinetic energy of the large object.

When atoms collide, there are no smaller particles for their kinetic energy to partition into. (This is not strictly true, but the nuclei and electrons in the atoms cannot absorb any arbitrary amount of energy, and in general don't dissipate the small amounts of kinetic energy involved in room-temperature collisions.)

Richard Barrans
Department of Physics and Astronomy
University of Wyoming


Hi Evren... the difference might be whether the chemistry book is considering a model (such as an 'ideal' gas), or actual materials. The statement may be correct if it's describing an assumption that underpins a model -- or it may just be an oversimplification, or a plain old error. Before I make any pronouncements about the book being right or wrong, can you send a little more info? Perhaps a scan of the page(s) in question, or a citation (if it is on Google books or something like that)?

Thanks,

Burr Zimmerman



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